This invention relates to a pH-reducing formulation, an active agent delivery system and a tampon comprising the same.
The normal, healthy human vagina is weakly acidic and has a pH of approximately 4.5. This acid condition of the vagina provides an effective barrier against the growth of pathogenic microorganisms normally associated with vaginal infection, because such microorganisms do not grow below a pH of about 5. If, however, the pH of the vagina becomes less acidic, i.e., higher than about 5, pathogenic microorganisms tend to multiply.
A change in pH of the vagina from the normal of about 4.5 to 5 to a more alkaline pH may be brought about by various vaginal conditions and may occur at any time during the menstrual cycle. During menstruation, in particular, the vagina becomes less acidic due to the presence of menstrual fluid which has a pH of from is about 7 to 8. As a result, the protective barrier provided by the normal acidic condition of the vagina becomes less effective, thereby providing an environment favorable to the growth of the pathogenic microorganisms.
To overcome the reduction in acidity of the vagina and to reestablish the desired normal acidic condition, different formulations and techniques have been developed. Such efforts have included the development of formulations such as solutions, jellies, powders, suppositories, and the like containing acidifying materials which are introduced into the vagina in their prepared form.
While the above-mentioned types of products have met with acceptance, they are subject to numerous disadvantages. The solutions, jellies, powders, and suppositories containing acidifying materials may be inconvenient to handle and apply and are not fully retained in the vagina and tend to escape. In addition, they do not have capacity for absorbing vaginal fluid which may be present in the vagina, particularly during menstruation. Therefore, to use such products during menstruation, it is also necessary to use at the same time a catamenial tampon or similar article.
Other attempts to lower the pH have included physically incorporating acidifying materials into absorbent products by coating, spraying, impregnating and the like, to impart to such products acidifying properties.
U.S. Pat. No. 4,431,427 to Lefren et al, discloses a tampon having incorporated therein one or more organic acids in combination with at least one of oligomer and polymer derivatives of the acids. The acids may be citric, gylcolic, malic, tartaric or lactic acid. The tampon is intended for maintaining a pH of about 4.5 to 2.5 in the fluids absorbed by the tampon during use, thereby inhibiting the growth of pathogenic bacteria in the tampon.
U.S. Pat. No. 4,661,101 to Sustmann discloses a catamenial tampon comprising a microbistatic fibrous absorbant core and an outer covering layer of a pH-regulating fibrous, cell lose material. The cellulose fibers are modified by carboxymethyl groups which are converted into their free acid form by treatment with an acid.
WO 91/08726 discloses a disposable sanitary napkin comprising a water permeable topsheet, an absorbent core and a water impermeable backsheet. The topsheet and/or backsheet comprise absorbable, hydrolyzable and biodegradable substances such as a lactic acid-based or glycolic acid-based polyester. This enhances the disposability of the napkin.
U.S. Pat. No. 6,020,453 to Larsson et al, discloses an absorbent article having a surface material, wherein the surface material includes a surface layer (being the outermost layer) which comprises a lactic acid-based polyester. The surface material is capable of excreting lactic acid to the surrounding urogenital region of menstruating women so as to establish a pH value of at most 4.0. The polyester has a molecular weight of at most 50,000 and the monomer/oligomer concentration is 5-30% by weight.
It is an object of the present invention to provide a novel formulation capable of reducing the pH in the menstruating vagina and/or in the tampon.
It is a further object of the invention to provide a novel delivery system for use with a feminine hygienic product, such as a tampon, to deliver an active agent to the female urogenital tract.
In a first aspect, the present invention provides a formulation effective in reducing the pH in a menstruating vagina or in a tampon inserted therein to below pH 5.5 comprising:
(a) 3-80% by weight of a solid organic acid polymer;
(b) 92-15% by weight of a solid organic acid; and
(c) 5-30% of a wetting agent.
The formulation of the invention is believed to be effective in reducing the pH to below pH 5.5 in a vagina during menstration and/or in a tampon inserted therein, and more preferably below pH 5.0, within a reasonable amount of time, such as within 0.5 hour. The components of the formulation are:
(a) an organic acid polymer which contributes to the long-term pH reduction;
(b) a solid organic acid which contributes to the immediate pH reduction; and
(c) a wetting agent for facilitating release of the organic acids.
The organic acid polymer of the formulation includes two or more monomers and is primarily non-acidic prior to hydrolysis. Examples of organic acid polymers include polylactic acid, polyglycolic acid and polymalic acid or copolymers of the above. A preferred organic acid polymer in the formulation of the invention is a polymer of lactic acid. Preferred polymers are L-lactide or DL-lactide (LD), a racemic mixture of a cyclic dimer of lactic acid, and polylactic acid (PLA) in the general range of 200-2000 MW. The organic acid polymer comprises 3-80% of the formulation, preferably 60-80%, most preferably 70-80%.
Examples of solid organic acids are citric, malic, maleic, fumaric, succinic, tartaric and oxalic acids. A preferred organic acid is citric acid. The organic acid comprises 92-15% of the formulation, and preferably 30-15%.
Examples of wetting agents which may be used in the formulation of the invention include glycerol, polyethylene glycol (PEG), polypropylene glycol (PPG) and surfactants with an HLB ranging from 10 to 18. Preferred wetting agents are glycerol and PEG-8000. The wetting agent comprises 5-30% of the formulation, and preferably 5-10%.
The formulation may comprise additional substances such as stabilizers, perfuming agents, preservatives, anti-oxidants, chelating agents, adsorbents, analgesic agents, anti-inflammatory agents, etc.
In a second aspect, the invention provides a delivery system for releasing an active agent it comprising:
(a) a deposition comprising the active agent; and
(b) a polymeric support on which the deposition is deposited.
The active agent may be any agent which performs a necessary function in the vagina such as an anti-bacterial, a pH-reducing or an deodorizing agent. Preferably, the active agent is a pH reducing formulation according to the invention, except that in this aspect of the invention, the wetting agent is optional.
The deposited formulation may include any polymer capable of producing and facilitating a coherent deposition on the polymeric support material. Such polymers include but are not limited to polyesters, olefins, cellulose and cellulose derivatives, PVA and PVP.
The polymeric support may be any polymeric material capable of serving as a support for the deposited material, and includes non-woven as well as woven materials. Examples of such support material include polypropylene, polyethylene, cellulose and cellulose derivatives or any other polymer which can be processed as a fiber.
A preferred shape of the polymeric support is a rectangular strip, which preferably consists of one or more layers, for example, 2-16 layers. Other shapes for the strip are also contemplated as part of the invention.
The delivery system of the invention is preferably used together with a catamenial tampon, as will be explained in more detail below.
Preferably, more than one delivery system will be placed in a tampon on different sides, so as to release the active agent in all directions.
Among the advantages of using the delivery system of the invention for releasing an active agent to the surrounding environment of the female urogenital tract is the contribution both to the economy of the manufacturing process of the tampon as well as to its reproducibility.
In a third aspect of the invention, there is provided A catamenial tampon for insertion in a human vagina comprising:
(a) an inner core comprising an absorbent material;
(b) an outer layer comprising a liquid permeable material; and
(c) a delivery system according to the invention.
Preferably, the delivery system incorporates the pH-reducing formulation of the invention.